Soft tissue medical implants such as mammary prostheses generally are made of silicone material for an elastomer shell and filling material disposed inside the shell. If the shell ruptures, either as a result of accidents or through crease-fold flaw or other modes of failure, the filling material escapes into the body. If the filling material is silicone gel, hydrogel, or gel made from natural biomaterial, the exposure of such a large volume of gel material in the body would pose a significant risk and complications for both long and short terms. The risks associated with any of the gel type material have been well documented and published in the literature.
If the filling material is saline, saline will excrete readily; however, the deflated shell must be removed and would require another surgery. In many cases, it has been reported that the small pieces and fragments of shell material might migrate to other areas causing further risks and complications.
If the filling material is hydrogel made from either synthetic or natural biopolymer, the long term risks or complications remain unknown because little data exists for tissue reactivity of these materials. Furthermore, since the chemistry and characteristics of the hydrogel are significantly different from conventional silicone gel, the acceptability of the gel made from material other than silicone still remains an issue with both physicians and patients.
Soft tissue implants, particularly breast implants, have gone through a considerable transition over several years with respect to the safety of silicone gel filling materials. As a result, a number of materials have been proposed to replace the silicone gel and saline which have been used over the past 30 years.
U.S. Pat. No. 4,731,081 to Tiffany et al., entire contents of which are incorporated herein by reference, discloses a surgically implantable mammary prosthesis that is rendered rupture-resistant by injecting a liquid with uniformly dispersed lubricating material into a flexible creasable shell during manufacture or surgical implantation. The lubricating material, such as polyvinylpyrrolidone, polyvinyl alcohol, hydroxyethyl starch, or lecithin is uniformly dispersed in a carrier inflating liquid such as normal saline.
U.S. Pat. No. 5,219,360 to Georgiade, entire contents of which are incorporated herein by reference, discloses a surgical mammary prosthesis containing a liquid-gel of cross-linked hyaluronic acid inside a medical grade elastomer, and a method of making a prosthesis containing such a liquid-gel. Because the gel used in the invention contains a nontoxic, nonantigenic, noninflammatory, biodegradable natural substance, problems attributed to or associated with previous silicone gel filled prostheses as a result of prosthesis rupture or leakage or “bleed” are avoided.
U.S. Pat. No. 5,282,857 to Perry et al., entire contents of which are incorporated herein by reference, discloses a medical implant comprising an outer envelope and a gel filler material, wherein the gel comprises water and a cellulose gelling agent. The gel in the implant may further contain a lubricating agent. The components of the gel are biocompatible and do not adversely affect human beings. Implants containing the lubricating agent have a decreased tendency of failure caused by internal friction on the envelope. The implants of the present invention have similar characteristics of the human breast.
U.S. Pat. No. 5,534,023 to Henley, entire contents of which are incorporated herein by reference, discloses an implantable prosthetic device having a biocompatible elastomeric shell and a polyphasic filler material consisting of gas-filled chambers or beads bathed in a biocompatible fluid. In a preferred embodiment the solid and gaseous phases of the filler comprise interconnecting flexible chains of small gas-filled beads. The gas-filled beads may be continuously extruded in a chain with a fiber of extrudate connecting the beads. In one embodiment, the extruded chains of beads are formed into a mass having the desired shape of the prostheses where they may be further crosslinked, then placed within an outer shell. The void space between the beads is filled with a biocompatible fluid such as saline.
U.S. Pat. No. 5,549,671 to Waybright et al., entire contents of which are incorporated herein by reference, discloses a fluid-filled mammary prosthesis for implantation beneath the skin of a patient comprising a shell and an adjunctive filler. The shell is preferably a closed silicone elastomer envelope having an interior volume and a valve for filling. The filler material is a mixture of a fluid such as saline and an adjunct consisting of a plurality of hollow silicone beads having two or more fenestrations within the wall of each bead which provide fluid communication between the outside of the bead and the hollow interior. The beads are packed into the shell prior to the introduction of fluid into the interior of the shell. The beads serve as a baffle to prevent unwanted hydraulic behavior of the fluid portion of the filler material and also serve to help maintain the anatomical profile of the implant. The hollow beads, which range in sizes from about 7/32 inch to ½ inch in inside diameter, may be conveniently made by injection molding. The adjunctive filler may be a plurality of beads of a particular size or a mixture of different sized beads.
U.S. Pat. No. 5,824,081 to Knapp et al., entire contents of which are incorporated herein by reference, discloses a tissue implant comprising a flexible shell, a fluid filler within the shell, a compound foam body disposed within the shell, the compound foam body comprising a distinct first foam region having a substantially uniform first cellular density throughout the first foam region, and a distinct second foam region having a substantially uniform second cellular density throughout the second foam region, the second cellular density being different than the first cellular density, and a cavity in the compound foam body adapted to provide a hydraulic reservoir for the fluid filler, the cavity being substantially larger than any cell.
U.S. Pat. No. 5,843,189 to Perouse, entire contents of which are incorporated herein by reference, discloses a breast prosthesis comprising a plurality of pockets filled with a liquid, wherein each of the pockets has, at rest, a predetermined configuration, and each of the pockets is delimited by a flexible membrane; and a holding device for holding the pockets against one another, wherein the pockets are formed integrally with one another so as to form at least one string.
U.S. Pat. No. 5,941,909 to Purkait, entire contents of which are incorporated herein by reference, discloses a new soft tissue implant filling material. The surgically implantable soft tissue implant filling material has good aesthetic properties, as measured by viscosity and elasticity. One embodiment of such a new filling material is a gel which comprises three components. The first component is a water soluble polymer or hydrogel that has a high molecular weight. Alternatively, the first component is both crosslinked and has a high molecular weight. The second component of the filling material is a water-soluble polymer that is eliminated rapidly through the kidneys upon subcutaneous release. The third component of this filling material is saline, which is used to dissolve the polymer and to adjust the osmolality of the polymer. In addition, a buffer may be added to the filling material to adjust the pH of the gel. One gel formulation of the present invention, in its preferred embodiment, consists of polyacrylamide and derivatives thereof.
None of the prior art patents recognize or addresses the critical and important issues which are involved in the selection of a suitable material that would provide a safe and effective implant filling material.